Researchers in the US are proposing adding a fourth light to traffic lights for driverless cars (writes Nick Flaherty).

The idea, from transportation engineers at North Carolina State University, is that a ‘white light’ would enable autonomous vehicles to help control traffic flow, and let human drivers know what’s going on.

In computational simulations, the new approach significantly improves travel times through intersections and reduces fuel consumption. Red lights will still mean stop, green will still mean go, yellow will warn that the light is about to turn red, while white lights will simply tell human drivers to follow the car in front of them.

The idea uses the fact that driverless cars communicate with each other and the computer controlling the traffic signal. When enough of them are approaching the intersection, it would activate the white light to coordinate them through the intersection.

When too many vehicles approaching the intersection are being controlled by drivers, the traffic lights would revert to the conventional green-yellow-red signal pattern.

The system could be used first with autonomous trucks. They have higher rates of autonomous vehicle adoption, so there could be an opportunity to implement a pilot project that could benefit port traffic, say, and commercial transportation.